The present application generally relates to integrated magnetic inductors.
Fully integrated radio frequency (RF) devices, including voltage controlled oscillators, low-noise amplifiers, and frequency filters, are used in mobile electronic devices. Typically, integrated RF devices have a large number of inductors that are incorporated into RF integrated circuits (RFICs). The inductors can consume a large area of the RFIC, and the inductors' quality (Q) factors can be important for power management and RF signal processing in the RFIC. Thus, the inductors can have an effect on the performance of the integrated RF device, which can affect the performance of the mobile electronic device incorporating the integrated RF device.
Previously, air core inductors (see e.g., FIG. 1A), for example, microelectromechanical systems (MEMS) and multi-stacked inductors, have been used with RF devices. A MEMS inductor, having a 15 μm thick, 2-turn coil and 40 μm suspension over a silicon (Si) substrate, showed a high Q factor of 27 at 2.6 GHz due to low substrate and ohmic losses. However, the inductor showed a small L-density of 11.2 nH/mm2 (L of 1.8 nH). In contrast, a two-stacked inductor with 9.5 total turns exhibited a high L-density of 283.7 nH/mm2 but a low Q factor of 9.8 at 2.3 GHz. The two-stacked inductor can have a low Q factor because the multi-stacked coil structure causes a large proximity effect and parasitic capacitance.
Instead of an air core inductor, a magnetic inductor can be used with RF devices. The magnetic inductor can use a film of a high permeability material located above the inductor coil (see e.g., FIG. 1B), below the inductor coil (see e.g., FIG. 1C) or both above and below the inductor coil (see e.g., FIG. 1D) to increase the L and Q factor of the inductor by increasing the magnetic flux and decreasing the coil resistance and parasitic capacitance. For example, a 2 μm thick CoZrTa magnetic inductor and a 15 μm thick Ni—Zn—Cu ferrite inductor showed about 28 and 1.1 times increases in L, respectively, compared to that of an air-core inductor. However, the magnetic inductors exhibited lower Q factors than that of the air-core inductor due to magnetic loss of the magnetic materials. Therefore, what is needed is an integrated magnetic inductor that can realize both high L-density and Q factor.